<!DOCTYPE html>
<html lang="zh-CN">

<head>
	<meta charset="UTF-8">
	<meta name="author" content="wangbo">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
</head>

<body>
	<script>
		function log(x, y) {
			y = y || 'World'
			console.log(x, y)
		}
		log('Hello') // Hello World
		log('Hello', 'China') // Hello China
		log('Hello', '') // Hello World

		function log(x, y = 'World') {
			console.log(x, y)
		}
		log('Hello') // Hello World
		log('Hello', 'China') // Hello China
		log('Hello', '') // Hello
	</script>
</body>

</html>